Method of shielding of fluorescent lighting fixtures

ABSTRACT

THIS PATENT DESCRIBES A NOVEL RADIO FREQUENCY SHIELDING FOR FLUORESCENT LIGHTS COMPRISING A CONTINUOUS STRIP OF FLEXIBLE FILM COATED WITH A LAYER WHICH IS ELECTRICALLY CONDUCTIVE AND CAPABLE OF TRANSMITTING LIGHT, SAID COATED FILM BEING FORMED INTO A CLOSURE AND SURROUDNING SAID FLUORESCENT LIGHT.

United States Patent Berton P. Levin Santa Monica, Calif.

Jan. 27, 1969 June 28, 1971 Sierracin Corporation, Sylmar. Calif.

lnventor Appl. No. Filed Patented Assignee METHOD OF SHIELDING OF FLUORESCENT LIGHTING FIXTURES 8 Claims, 6 Drawing Figs.

US. Cl 29/592, 174/35, 240/114, 313/1 13, 313/355 Int. Cl H05k 9/00 Field of Search 174/35, 36, 68 (C); 29/592, 624; 240/5l.l l, l 1.4, 46.19, 46.49,46.55;313/110, 112,113, 355,356,312, 313; 315/85; 350/311 [56] References Cited UNITED STATES PATENTS 2,509,979 5/1950 Marti l74/35(.4)UX 2,522,072 9/1950 Tierney,.lr. l74/35(.4)

Primary Examiner-Darrell L. Clay Attorney-Lyon & Lyon ABSTRACT: This patent describes a novel radio frequency shielding for fluorescent lights comprising a continuous strip of flexible film coated with a layer which is electrically conductive and capable of transmitting light, said coated film being formed into a closure and surrounding said fluorescent light.

METHOD OF SHIELDING OF FLUORESCENT LIGHTING FIXTURES BACKGROUND OF THE INVENTION There has recently been an increased interest in radio frequency shielding of fluorescent lighting fixtures. To date, the favorite approach has been to provide an electrically conductive layer on the diffusing glass panel located generally between the fluorescent tubes and the illuminated room or area. The diffusing glass panel is generally flat, rectangular and made of some transparent lightweight material such as glass or acrylic plastic. The panel is generally directly attached to the fixture which holds the fluorescent tubes. The electrically conductive layer on the panel is normally either a thin transparent electrical coating deposited for example by conventional vacuum deposition techniques, or the metal coating can be made of a matrix or array of woven wire or wire in some geometric pattern which permits reasonable light transmission and still provides the necessary radio frequency attenuation.

More recently it has been proposed that radio frequency shielding. be provided directly around the individual fluorescent tube. The initial concepts were based on a transparent tube of lightweight material which would accommodate the fluorescent tube inside its interior. This shielding tube would then be metallized either on its inner or outer surface and equipped with appropriate end caps to ground the electrically conductive coating. The difficulty with this approach is the cost involved in handling the shielding tubes in the various steps required inside and outside the metallizing chamber.

The present invention is believed to represent a substantial advance in the art in that there is now provided the advantages of continuous coating to the problem of radio frequency shielding. It is, therefore, anticipated that the present invention will be widely adopted in the applications whereradio frequency shielding of fluorescent lighting fixtures is required.

SUMMARY OF THE INVENTION Briefly, the present invention comprises a novel radio frequency shielding for fluorescent lights comprising a continuous strip of flexible film coated with a layer which is electrically conductive and capable of transmitting light, said coated film being cut to required length, formed into a closure, usually cylindrical, and adapted to surround a fluorescent light.

It is an object of the present invention to provide anovel technique for the radio frequency shielding of fluorescent lighting fixtures.

It is another object of the present invention to provide radio frequency shielding of fluorescent light fixtures wherein the shielding material is prepared in a manner which permits the use of continuous coating techniques.

These and other objects and advantages of the invention will be apparent from the more detailed description which follows taken in conjunction with the accompanying drawings.

DESCRIPTION OF PREFERRED EMBODIMENTS Turning to the drawings:

FIG. 1 shows in roll form the type of metallized flexible film used to form the'shield of the present invention;

FIG. 2 shows the formation of a shield from the metallized flexible film with a straight line joint;

FIG. 3 shows the formation of a shield from the metallized flexible film with a spiral joint;

FIG. 4 shows one type of joint connection which can be used in this invention;

FIG. 5 shows another type of joint connection which is useful in my invention; and

FIG. 6 shows an end perspective view of the shield with electrical connections to the fluorescent tube contained therein.

Turning to the drawings in detail, a continuous strip of thin film, for example plastic, is coated with a metal layer of appropriate light transmission and electrical conductivity. The particular coating technique is not pertinent to the present invention and any of those continuous techniques familiar to those skilled in the art may be utilized. The resultant metallized strip 10 can then be formed into the desired closure shape with either butt joints or overlapping joints in either straight line I2 or spiral configuration 14, as shown in the drawings. In either case, the joint can be secured by bonding with some electrically conductive adhesive or with a strip of similarly coated transparent film. If the bonding of the joint is achieved at the cost of reduced light transmission along the joint, the penalty is lessened by making the bond line extremely narrow, on the order of about a sixteenth of an inch so that the loss of light is negligible, and orienting bond line in fixture to be on side of tube opposite region to be illuminated.

In FIG. 4, the shield is formed from the metallized flexible film 16 with the conductive coating on the inner or concave surface. The butt ends of film 16 are joined with an opaque conductive metal-loaded resin 18. A reinforcing strip 20 is attached to the outside of the joint by an adhesive.

In FIG. 5, a conductive adhesive strip 22 is used to make the joint connection of the metallized film 24. The strip 22 can be reinforced by a strip 26 of, for example, copper foil.

The grounding connection for the closure can be achieved in a number of ways. One preferred way is by first dipping the ends of the joint-bonded tube in a conductive resin or a low temperature melting point metal bath (for example one of the several Cerro alloys, e.g., p. l9 of Catalog No. 33, Claude Michael Inc., Glendale, California). This forms a metal overcoat 28 at each end of the shielding tube 30. Then, tapered conductive plugs 32 in the shape of a frustoconical section are inserted into the metallized ends of the tube 30 to provide hoop expansion forces to keep the tube 30 rigidly expanded. The plugs 32 may be fitted with spring clips 34 for clamping to the metal-capped terminal ends 36 of the fluorescent tube 38, thus providing a radial, noncontact standoff between the fluorescent tube 38 and the shielding tube 30, and a means of providing an electrical path to ground for the shield. The tinning on the ends of the shielding also permits the rough treatment necessary in repeated removal and insertion of the plugs for tube replacement without risking damage to the fragile conductive coating.

It will be understood that the present invention is not limited to the radio frequency shielding of any particular type of fluorescent tube. Likewise, the invention may be practiced using any type of flexible film having substantial transparency such as the common plastic types such as polyethylene terephthalate, polytetrafluoroethylene, and the clear cellulose esters. The conductive coatings are usually metals such as gold, silver, and the like. The only limitation on the conductive coating is that it has at least some significant light transmission. Those skilled in the art will be able, from what has been said herein, to select the best conductive metal for any given application by a minimum of routine cost calculations and tests. I

Having fully described the invention it is intended that it only be limited by the lawful scope of the appended claims.

Iclaim:

1. A process for forming a radio frequency shield for fluorescent lights comprising coating a continuous strip of flexible, translucent film with an electrically conductive metal layer capable of transmitting light and forming the resulting coated continuous strip into a closure, said closure having two open ends.

2. The process of claim I wherein the step for forming comprises folding a length of said continuous strip into a generally cylindrical tube and joining the opposite sides of said strip to form a longitudinal joint.

3. The process of claim 2 wherein the joining step comprises applying a conductive adhesive strip to the opposite sides.

4. The process of claim 1 wherein the step for forming comprises spirally winding a length of said continuous strip to form a generally cylindrical tube and joining the opposite sides of said strip to form a longitudinal joint.

5. The process of claim 2 wherein the joining step comprises applying a conductive resin to said opposite sides.

6. The process of claim 1 wherein the step for forming comprises folding a length of the coated strip into a generally cylindrical tube with said conductive layer located on the interior of said tube.

7. The process of claim 6 having the additional step of inserting a conductive frustoconical sleeve into each open end of said closure.

8. A process for shielding a fluorescent lighting tube comprising coating a continuous strip of flexible translucent film with an electrically conductive layer capable of transmitting light; forming the resulting coated continuous strip into a generally cylindrical tube with the conductive layer on the interior of the tube; affixing a conductive frustoconical sleeve onto one end of said fluorescent tube by means of a conductive spring slip; disposing the cylindrical tube over the fluorescent lighting tube and over a portion of the frustoconical sleeve; placing a second conductive frustoconical section into the other end of said cylindrical tube; and affixing the second conductive section onto the other end of said fluorescent tube. 

